The following relates generally to illumination arts, lighting arts, solid state lighting arts, and related arts, and find particular application in conjunction with the use of reflectors in LED decorative lamps. However, it is to be appreciated that the present exemplary embodiments are amenable to other like applications.
Incandescent light bulbs are widely used in household and commercial lighting, for portable lighting, such as table lamps, car headlamps, and flashlights, and for decorative and advertising lighting. Incandescent lamps are generally omni-directional light sources capable of providing substantially uniform intensity distribution over a wide angle in the far field (greater than 1 meter away from the lamp) and find diverse applications such as in desk lamps, table lamps, decorative lamps, chandeliers, ceiling fixtures, and other applications where a uniform distribution of light in all directions is desired.
Incandescent light bulb packages include a light source comprising an incandescent filament within a glass enclosure. However, the incandescent filaments are fragile and tend to gradually degrade during a lifetime of a bulb causing the useful light output generated by the filaments to decrease over time. The increasing fragility of the filament with age eventually leads to breakage. Typical incandescent bulbs have a mean life of 500 to 4,000 hours.
Light emitting diodes (LEDs) are now being implemented as an attractive alternative light source in a light bulb package. A low-power, solid state LED light could last up to 100,000 hours (eleven years), far outlasting the life of a typical incandescent bulb. When the LED degrades to half of its original intensity after 100,000 hours, it continues operating with a diminished output. Even with this diminished output, LEDs are still ten times more energy efficient than incandescent bulbs, and about twice as efficient as fluorescent lamps. Besides producing little heat and being energy efficient, LEDs are solid-state devices with no moving parts. LED characteristics do not change significantly with age and they are not easily damaged by shock or vibration. This makes LED lighting systems very reliable. The small shape and low heat generation enables LED lighting systems to take on various shapes and sizes.
Widespread use of the LED lighting systems has been limited because the consumers are accustomed to seeing and purchasing the traditional incandescent bulb lights. The number of various incandescent light bulb packages on the market is tremendous. Particularly, decorative light bulbs are seen in various shapes, such as globe, candle, torpedo, prism, star, etc. to suit decorative requirements. Decorative incandescent bulbs are used in many different kinds of lighting applications including chandeliers, outdoor lighting, and many other types of indoor, outdoor, or special accent lighting.
One approach to making LED light bulbs more commercially attractive has been to directly retrofit the LED into the existing light package. LED devices have been developed with one or more light emitting diodes for emitting light. The diodes include a positive terminal and negative terminal for electrical conduction. The device further may include a lead frame electrically coupled to the positive and negative terminals of the diodes. The lead frame connects the diodes to an outer circuitry such as a power supply, such that when activated, the lead frame causes the diodes to emit light. The device may further comprise a light transmissive dome encapsulating the diodes.
As mentioned above, unlike an incandescent filament in traditional bulbs, an LED is an inherently directional light source, as they are a flat device emitting from only one side. However, LEDs can be modified with individual optics and may be arranged in a way to approximate the broader light distribution of an incandescent lamp. Lenses are also commonly used in decorative lighting applications to gather and control the light produced by the lamp.
Typically, polycarbonate (“PC”) lenses are implemented to adjust the light distribution and obtain a larger beam angle. PC lenses comprise transparent or semi-transparent plastic material. Since PC has a high transmission and a relatively low cost, it is widely used to make low-cost lenses for LED products. The PC lens will create a larger beam angle; however, transmission loss is about 15-20%, resulting in a low lumen per watt (lm/W) of the LED decorative lamp system, such as only 35-45 lm/W. Accordingly, there is a need for a means of adjusting light distribution while minimizing transmission loss.